How drying preserves food

Appears in

Canning for a New Generation by Liana Krissoff

By Liana Krissoff

Published 2010

About

This one’s easy: Microorganisms need water. Remove the water, and they meet a horrible end.

Botulism

Botulism poisoning, a very serious and sometimes deadly illness, is most commonly the result of ingesting improperly canned low-acid foods like plain unpickled green beans. All the canned foods here are high-acid fruits or acidulated vegetables, so botulism isn’t really an issue, but let’s discuss the bacterium that causes it, Clostridium botulinum, in a bit more detail anyway. While the bacterium itself is killed by boiling temperatures, its spores survive much higher temperatures than can be achieved in a boiling-water bath and are actually activated in oxygenless environments like the inside of a canning jar. This means that even though a food has been boiled, processed, and sealed, it may still contain the spores whose activation and growth produce a toxin that can cause botulism poisoning. The spores cannot, however, survive in high-acid environments—that is, in foods that have a pH lower than 4.6. All of the canning recipes in this book result in foods with pH levels that are well below 4.6; for the pickling recipes using vinegar, it’s important that you use the vinegar called for in the recipe, with the acidity percentage specified.

Low-acid foods, or vegetables that have not been acidulated (pickled) to a proper degree, must be canned in a pressure canner, which can process jars at temperatures higher than that of boiling water, high enough to kill bacteria as well as the spores of Clostridium botulinum. Do not process nonacidulated vegetables or meats in anything other than a pressure canner. None of the canning recipes in this book requires a pressure canner because they are all for high-acid foods.